Process of restoring rubber



(No Model.) 2 Sheets-Sheet 1 N. C. MITCHELL. PROGB$S 0F RESTORINGRUBBER.

No. 420,820. Patented Feb. 4. 1890.

u vztans Pholmljlhcgmphm, Washington, D. c.

2 Sheets-Sheet 2'.

(No Model.)

N. 0. MITCHELL. PROCESS OF RESTORING RUBBER.

Patented Feb. 4, 1890.

N. Fl-IIERSv Pholo-L'llhngnphar, Wmhingham D c.

. keep the rubber in a moist condition.

UNITED STATES FATENT OFFICE.

NATHANIEL C. MITCHELL, PHILADELPHIA, PENNSYLVANIA.

PROCESS OF RESTORING RUBB ER.

SPECIFICATION forming part of Letters Patent No. 420,820, dated February4, 1890. Application filed September 20, 1889. Serial No. 324,583. (Nomodel.)

To all 'whom it may concern.-

Be it known that I, NATHANIEL CHAPMAN MITCHELL, of Philadelphia, in thecounty of Philadelphia and State of Pennsylvania, have invented a newand useful Improvement in the Process of Restoring Rubber, whichimprovement is fully set forth in the following specification.

This invention has reference to the treatment of rubber wastesuch as oldboots and shoes-for the purpose of recovering therefrom the rubber as amarketable product.

In the recovery of rubber from rubber waste the old stock, afterbeinggroundbetween cracker-rolls and freed from foreign matters as metal,sand, and fiber-is exposed to the action of heat, preferably steam-heat,for the purpose of devulcanization, and it is to this portion of theoperation-namely, the devulcanization and desulphurization of therubber-that the present invention has particular reference. The steamacts, mainly, to soften the rubber, and has but little effect inremoving the sulphur. I have discovered that desulphurization may beeffected by mixing with the rubber a small quantity of sulphide ofcalcium previously to the treatment with steam. \Vhen calcium sulphideis used alone, it requires a very high degree of heat to effectdesulphurization, which high degree of heat dries the rubber to aninjurious extent. It is therefore desirable to mix wit-h the calciumsulphide some substance which will For this purpose it is preferred touse heavy petroleum. I usually employ seven pints of the mixture ofpetroleum and sulphide of calcium to two hundred pounds of rubber scrap,and seven pints of the fluid contains onequarter of a pound of thesulphide.

It has heretofore been a very tedious and difficult operation to fillthe devulcanizer with a full charge of rubber, and a still moredifficult one to remove the charge after treatment, inasmuch as therubber becomes compacted and set by the action of the steam. It has beencustomary to introduce the rubber in pans or Vessels, which rest upon aWagon or truck rolled into the devulcanizer; but by this means, inaddition to the difficulty of handling, it is impossible to utilizeanything like the full capacity of the devulcanizer, or to direct thesteam through all parts of the mass.

It is an object of this invention to effect devulcanization in bulkthatis to say, with the rubber charged directly into the cylinder andresting on the bottom thereof, which has never before been accomplished,so far as I am aware. By so doing a more thorough and uniformdistribution of the steam'can be effected, and when it is desired todraw air through it, as presently described, this can be accomplishedwithout difficulty. It would b obviously impracticable to maintain sucha circulation through all parts of a mass con tained in pans, and theresult would not be uniform.

The devulcanizer employed by me is a long cylinder disposedhorizontally, about five feet in,- diameter, and having a capacity of,say, from sixteen thousand to twenty-eight thousand pounds, more orless. It is provided with a perforated false bottom for admission anddistribution of the steam, and a pair of rails extend lengthwise of thecylinder. On these rails are run a series of hooks of specialconstruction, as hereinafter more fully set fort-h. In charging, one ofthese hooks, to the end of which is attachedachain,is placed at the endof the cylinder, and a car filled with rubber to be treated is run inand its load emptied into the cylinder by means of special deviceshereinafter described. This is repeated until the cylinder is filled toa distance of, say, four or five feet, when a second hook is introduced,and so on until the cylinder is fully charged and the rubber fills itsolidly from end to end and to within ashort distance'of the top. Thecylinderis provided with a removable head, which is now swung into placeand secured by bolts. Steam is then turned 011 and the valves adjustedto maintain a pressure of from one hundred to one hundred and twentypounds. Under these conditions the hydrocarbon oil combines with therubber and the sulphide of calcium removes the free sulphur, combiningwith it to form persulphide of calcium. This is to a large extentremoved in the water of condensation. According to the present inventionthere is a constant circulation of steam through the devulcanizer, thesteam passing through the perforations in the false bottom (by which itis diffused uniformly through the mass of rubber) and escaping through asuitable pipe, which leads to a condenser. After the operation hascontinued a sufficient tin1e-say for thirty-six hoursthe cylinder isblown off from the top and bottom valves, and so soon as the pressure isreduced to the normal a vacuum-pump is connected with a suitable pipeopening preferably into the bot tom of the cylinder, drawing air throughthe mass of rubber from top to bottom. The operation of drawing airthrough the rubber continues for about sixty minutes. This is a veryimportant ste p in the process, since thereby much time is saved indrying, to effect which the residual heat of the devulcanizer is thusutilized, and the latter, moreover, is partly cooled down. The next stepis the removal of the devuleanized rubber, which is effected by drawingout successively the several hooks, each hook carrying in front of it amass of rubber, which is immediately broken up and passed throughdisintegrating-rolls preparatory to drying and sheeting. The use of theperforated false bottom and the uniform distribution of the heat therebyeffected is particularly advantageous in that it prevents unequalexpansion and contraction of the devulcanizer, which in a vessel of suchdimensions it is of great importance to avoid. Moreover, as the steam isconstantly passing in and out the temperature of the devulcanizer at thetop is practically the same as at the bottom.

In order that the said invention may be fully understood, I will proceedto describe the same in connection with the accompanyin g drawings,which illustrate apparatus used in practicing the said invention.

Figure I is a side elevation of a devulcanizing apparatus constructed inaccordance with the invention, the cylinder being partly broken away toshow the interior. Fig. 11 is a plan View thereof, and Fig. III across-section of the cylinder. Fig. IV illustrates in elevation theremovable head; and Fig. V is a perspective view of one of thedischargehooks, on a larger scale than the other figures.

A represents the ,devulcanizer. It is provided with a head B, which,instead of being hinged to the vessel, preferably, should be entirelyseparate therefrom, and during the process of loading and unloading canbe swung out of the way by means of an overder the bottom cl from end toend of the cylinder. (See Fig. 11.) A car or truck is arranged to run onrails a into the interior of cylinder A, and by means of this car ortruck the operation of charging is carried on. The car 0 is providedwith a follower f, extending lengthwise across the body thereof, andadapted to push off the load of rubber from the forward end. Thefollower f is attached to a rod g, which passes through a guide-hole inthe tail-board h of the car. To the outer end of rod gis attached a ropei, which passes over a pulley j on car C,and then over a pulley1,beingattached atits end to a windlass, (not shown in the drawings,) by meansof which the follower f can be pushed forward, discharging its load ofrubber scraps into the devulcanizer.

The construction of the hooks G is shown in Fig. V. The hook is somewhatsimilar in form to an inverted rake. It is composed mainly of stout barsof wrought-iron about half an inch thick and two inches wide. The rearor upright portion of the hook is formed of bars 75 bentinto U shape.These are firmly braced by cross-bars I, which are secured to thevertical bars by angledrons Z. The tongue m is bolted at its rear end tothe uprights, and at its forward end has an eye to which is attached adraft-chain n. The side pieces 0 are bolted at one end to the outeruprights 7t and at the other to the shank of tongue m. Additionaloblique braces '11, and o are provided to strengthen the structure. Thebottom pieces 19 also constitute runners for sliding the hooks overrails c. The whole struct ure is open, so as not to interfere with thecirculation of the steam, and, while comparatively light and occupyingsmall space Within the devulcanizer, has ample strength for the workrequired.

The method of charging the cylinder A is clearly shown in Fig. I. Thefirst hook G being placed in position in the extreme end of thecylinder, the space over and in front of it is filled by means of car 0for a distance lengthwise of the cylinder, say, of five feet. Anotherhook is then placed in position and the charging proceeds as before.Then the cylinder is charged to its utmost capacity, the rubber fillingit in a continuous mass from end to end, platform I at the mouth of thecylinder is removed, and head B is swung into place and securely boltedto the cylinder. Steam is then turned on through pipe e by means of cockr, and is admitted to the space beneath false bottom (Z, and by theperforations in the latter it is diffused through all parts of the massof rubber. The steam-exit pipe 9' is always open, so that the steam isconstantly circulating through the cylinder, instead. of remainingstagnant therein. This is found to be an important improvement andrenders the operation of devulcanization much more thorough. Moreover,it reduces the amount of condensation-in the cylinder. The water ofcondensation formed therein is collected in the space beneath theperforated bottom, which space is constantly drained by pipe .9, whichis provided with a steanrtrap ITO to prevent escape of steam. Tofacilitate the drainage the cylinder is preferably slightly inclinedtoward its forward end. Vhen the operation of devulcanization iscomplete, pipe 6 is closed and exhaust-pipes t and uare opened,blowingoff the steam at both top and the top thereof.

bottom. When the pressure-gage indicates zero, pipe v, which leads tothe bottom of the cylinder and is connected with steam-pipe e, is openedand avacuum-pump put into operation,by means of which heated air isdrawn into the cylinder through pipe 10, leading to The air is drawnthrough the mass of rubber from top to bottom, removingv a great portionof the moisture. When it enters the cylinder, which is at a very hightemperature within, the air is still further heated thereby, thusperforming its work more efficiently. In addition to the utilization ofthe residual heat of the devulcanizer to dry the rubber, this operationis advantageous in that it reduces the temperature of the latter to suchan extent that when the head- 13 is removed the workmen can at onceproceed to withdraw the hooks G. Prior to the adoption of this plan itrequired about five hours to blow off the cylinder, and even then, whenthe head was removed, considerable steam remained, and the heat was sointense that the operation of discharging could not begin for some time.Now the whole operation subsequent to the shutting off of the steamrequires only two hours and a half. When the head B is removed, themovable platform I is again rolled to the mouth of the cylinder, thedraft-chain n of the first hook is hooked on to a chain attached to theWindlass and the hook drawn on to the platform, carrying with it themass of rubber in front of its prongs. This mass is a com,- pact lump,which is broken up into smaller pieces and removed by trucks to thecrackerrolls for disintegration prior to drying and sheeting. The nexthook is drawn out in like manner, and so on with all the others, untilthe cylinder is empty.

I have given. in the foregoing description what is regarded as the bestmode of carry-- ing the invention into effect; but I wish it to beunderstood that the said invention is not limited to the precise detailsdescribed, which could obviously be modified or varied within widelimits without departing from the principle of the invention. It isfurther obvious that some of the improvements described could beomitted, though to obtain the best results it is desirable to employtheinvention in its entirety.

No claim is made herein to the apparatus described and shown, as thisforms the subject-- matter of a divisional application filed November23, 1889, Serial No. 331,358.

Having now fully described my said inven tion, what I claim, and desireto secure byLetters Patent, is-

1. The herein-described process of devulcanizin g and desulphurizing oldrubber,which process consists in commingling with the rubber scrapsheavy oil and calcium sulphide,

and then heating the mass with live steam, as set forth.

2. In the process of restoring old rubber, the improvement consisting inmixing the rubber with sulphide of calcium and then subjecting it to theaction of heat, substantially as described.

3. The herein-described process of devulcanizing and desulphurizing oldrubber,which process consists in mixing therewith heavy oil and calciumsulphide, and subjecting the mass to the action of live steam underpressure in a close vessel, as set forth.

4. In the art of devuloanizing rubber, the improvement consisting inreducing the stock to small fragments and maintaining a con stantcirculation of steam through the same until thoroughly softened anddevulcanized, substantially as described.

5. In the devulcanization of rubber, the improvement consisting inmaintaining through the mass of stock in a reduced or fragmentarycondition a circulation of steam at substantially the pressurehereinbefore set forth.

6. The process of restoring old rubber,which process consists insubjecting the rubber to the action of live steam in a' close vesseluntil thoroughly softened and devulcanized, blowing off the steam, andthen passing a current of air through the mass, substantially asdescribed.

7. The herein-described process of restoring rubber, which processconsists in mixing the rubber, after reduction to small pieces, withheavy oil and sulphide of calcium, then subjecting it to the action ofsteam until devulcanization is completed, and finally drawing airthrough the mass before itsremoval from the devulcanizer, substantiallyas set forth.

In testimony whereof I have signed this specification in the presence oftwo subscribing witnesses.

NATHANIEL O. MITCHELL.

WVitnesses:

PHILIP MAURO, C. W. ORoAsnILL.

IIO

